1. Field of the Invention
The present invention relates to an accuracy measuring apparatus for measuring the run-out accuracy of a spindle and the feed linearity of a feed mechanism in a machine tool.
2. Description of Related Art
Before machine tools are shipped from a machine tool maker to users, the run-out accuracy of a spindle and the feed linearity of a feed mechanism, which directly influence the machining accuracy of the machine tools, are generally checked and adjusted to satisfy predetermined reference levels.
One exemplary method for measuring the run-out accuracy is such that a cylindrical test tool having a highly accurately finished outer circumference or a test tool having a spherical ball attached to a shaft is fitted in a tapered portion of a spindle hole and rotated about an axis thereof, and an offset of the outer circumference of the test tool is measured, whereby the run-out of the test tool is detected on the basis of the measured offset. Another known method is such that a parabolic mirror having a small diameter is attached to an end of the spindle on the center axis of the spindle, then a light beam emitted from a microscope with a light axis generally aligned with the center axis of the spindle is reflected on the parabolic mirror, and the reflected light beam is introduced into the microscope to be photographed on a film, whereby the run-out of the center axis is determined on the basis of the results of the photographing.
One known method for measuring the feed linearity of the feed mechanism is such that a straightedge is attached to a slide to be fed by a feed mechanism, and a measurement surface of the straightedge is detected by a dial indicator while the slide is fed. Another know method is such that a reflection mirror is attached to a slide to be fed, then a light beam is projected from an autocollimator onto the reflection mirror and the light beam reflected on the reflection mirror is received by the autocollimator while the slide is fed, whereby the feed linearity is determined on the basis of a change in reflection angle.
However, the aforesaid measuring methods are merely capable of measuring either the run-out accuracy or the feed linearity. Therefore, measuring apparatuses should separately be prepared for measuring the run-out accuracy and the feed linearity. Thus, these methods are poor in efficiency, and costly.
In view of the foregoing, it is an object of the present invention to provide an accuracy measuring apparatus which is capable of efficiently measuring the accuracies of a machine tool at low costs.